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TI-2026-32068 Aliases CVE-2026-44040GHSA-j37g-g7hg-vhg6

UltraVNC vncauth.c uses time-seeded libc rand() to generate VNC authentication challenge bytes

Priority LOW 29CWE-338Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
—
Confidentiality · integrity · availability
Low · Low · None
Fix status
No fix listed

Attack profile from CVSS 3.1 · NVD. Fix status from CNA.

Summary

UltraVNC through 1.8.2.2 uses a cryptographically weak pseudo-random number generator to produce VNC authentication challenge bytes. In rfb/vncauth.c:119-129, the vncRandomBytes() function seeds libc rand() with time(0) + getpid() + rand() and generates a 16-byte challenge. The combined seed space is approximately 31 bits (libc rand() internal state) and is entirely determined by publicly-observable values (wall-clock time and process ID). An attacker who can observe the authentication exchange can enumerate the seed space and predict the challenge within seconds, enabling forgery or offline brute-forcing of responses. Note: on Windows, the active code path may use vncEncryptBytes2.cpp which calls CryptGenRandom; reachability on shipped Windows binaries requires compile-graph verification and is under investigation.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00397 34th percentileScored 2026-11-07
Fix No fix listed No fixed version in the sources yet

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
uvncUltraVNCup to 1.8.2.2—No fix listedCNA
  • UltraVNC Vendoruvnc Affected up to 1.8.2.2 Fixed in — No fix listed CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:uvnc:ultravnc:*:*:*:*:*:*:*:*up to 1.8.2.2Vulnerableuvnc
  • cpe:2.3:a:uvnc:ultravnc:*:*:*:*:*:*:*:* Versions up to 1.8.2.2 Vulnerable ·uvnc

Remediation

No fixed version listed by the sources yet.

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-44040
  2. 2026-10-03 Alias added: GHSA-j37g-g7hg-vhg6

References

Advisory 1

Other 2

  • TI-2020-19268 UltraVNC Launcher 1.2.4.0 - 'RepeaterHost' Denial of Service CVSS 4.0MEDIUM 6.7
  • TI-2026-04323 UltraVNC Service version.dll uncontrolled search path CVSS 4.0HIGH 7.3
  • TI-2020-19267 UltraVNC Launcher 1.2.4.0 - 'Password' Denial of Service CVSS 4.0MEDIUM 6.7
  • TI-2026-06899 UltraVNC repeater HTTP server global buffer overflow via long URI (pre-auth RCE) CVSS 4.0CRITICAL 9.3
  • TI-2019-05946 Heap-based buffer overflow in Kaspersky Lab UltraVNC CVSS 3.1CRITICAL 9.8
  • TI-2019-05945 Heap-based buffer overflow in Kaspersky Lab UltraVNC CVSS 3.1CRITICAL 9.8
See all 36 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences